Different Perspectives on Accident Causation: Some Accident Case Studies

Table 1 lists some well known case studies. These are events or accidents which have been in the public eye at some time and have been the subject of investigations, enquiries, newspaper reports and so on. They are drawn from various areas: aircrashes, failures of chemical plant, a football stadium disaster and others. Generally, there are detailed published accounts and analyses of these events which describe how they happened. These are listed in the references. Table 1 also lists some different perspectives that have been taken, at various times, by others in considering the causes of the events. These are illustrated in Figure 1.1. My purpose here is to look briefly at these perspectives for the events described. At this stage I am not trying to show that some may be right and others wrong, but simply to show that different individuals and organisations tend to take different views. This raises the question as to whether a search for more complete descriptions might not suggest practical consequences for risks and safety.

Although the case studies are drawn from various areas, I am assuming that the lessons which can be learnt are independent of the area and can be applied to other areas, i.e. I assume that the underlying causes of accidents, events and incidents will cover similar, general types in the various areas considered. Consequently I have not chosen chemical plant incidents, exclusively, but events or incidents which I consider best illustrate the different perspectives. I assume that the conclusions drawn will be applicable to chemical plant incidents in a general sense, e.g. that weak management will lead to problems irrespective of the area which is managed weakly.

1.1 HARDWARE

1.1.1 Case Study 1

A warehouse fire involving reactive chemicals is described in the Health and Safety Executive's (HSE) investigation into the fire at Allied Colloids Ltd, Bradford on 21 July 1992. In Table 1 this incident is listed under the perspectives Technical issues highlighted – How did it happen? and In what sequence?

The HSE investigation report includes lessons learnt and considers the management of health and safety, but emphasises both the possible sequences of events and the scientific basis used to explain how the fire happened. The following points from the report give an indication of the nature of the investigation.

• Numerous employees who had been directly involved with the incident were identified and interviewed.

• Efforts were concentrated on gaining an appreciation of the range and quantities of chemicals involved and how and where they were stored.

• The scientific investigation examined the properties of and interactions between the materials stored, the nature of the products of combustion and the general spread of the fire. Extensive studies were carried out on a number of chemical samples from the site.

• The investigation also examined potential sources of heat capable of raising the temperature of the contents of reactive chemical kegs to the point where sufficient material would decompose to cause that package to fail.

• The investigation looked at the failure characteristics of the kegs and the spread of the fire through the warehouse. A technique known as computational fluid dynamics was used to help quantify the heat sources.

HSE investigations soon established that the stores contained a self-reactive substance which was thermally unstable and capable of undergoing violent decomposition at relatively low temperatures. The incident started when two or three kegs of this substance ruptured. These were stored on the top shelf of the racking in the warehouse, close to the steam condensate return line and a roof light panel. The sun would not have been shining directly on the kegs, and it was concluded that a malfunction of the steam heating system or operator error caused the condensate pipe to be hot.

1.1.2 Case Study 2

Other incident investigations, such as the catastrophic failure of an ammonia/air mixer described by Verduijn follow a similar form. There is an emphasis on establishing the sequence of events and the direct technical causes, which include the chemical-reactions involved and any failures of chemical plant items and also on describing lessons learnt.

1.1.3 Case Study 3

The investigation of the Hillsborough Football stadium disaster by the Health and Safety Executive focused on technical aspects of the disaster, including metallurgical examination of crash barriers, collapse load calculations and development of a model to predict crowd pressures, among other issues. Ninety-five people died from crush asphyxia because of severe overcrowding. The investigation provided important evidence in determining what happened at Hillsborough and enabled the elimination of some of the theories put forward in the aftermath of the disaster.

1.1.4 Case Study 4

Clearly, after a tragic incident there is a desire to find out what happened. This can sometimes lead to alternative technical explanations of the cause of the incident (even after the court of enquiry into the event). On 11 July 1978 a disaster occurred at a campsite in Spain in which over 200 people lost their lives due to fire and explosions involving a road tanker carrying liquefied petroleum gas which burst open and lost its contents. The exact events which occurred were the subject of a debate in the literature which centred around whether or not the tanker exploded due to over-loading followed by sunshine raising the tank temperature; whether a vehicle crash occurred; or, finally, whether the tanker was first engulfed in a fire which subsequently caused the explosion. Such debates and investigations are important...